FIG. 6 shows a conventional detector of a rotation angle and torque. Gear 18 is mounted to an input shaft (not shown) of a torsion bar. Gear 21 engaging with gear 18 includes round-shaped code plate 20 having numbers of magnetic poles. Code plate 20 rotates following the rotation of the input shaft. Detecting element 22 of magnetism counts the number of poles rotating, thereby detecting a rotation angle of the input shaft. Gear 42 is mounted to an output shaft (not shown) of the torsion bar, and detects a rotation angle of the output shaft in the same manner as discussed above. When torque works to the torsion bar, thereby producing torsion on the shaft, a comparison of rotation angles between the input shaft and the output shaft will detect the torque.
However, a more accurate rotation angle requires code plate 20 to have greater numbers of poles, so that the dimensions of the detector will become greater. Placement of detecting elements 22 in a radius direction on code plate 20 will also enlarge the detector. The conventional detector discussed above cannot detect an absolute rotation angle.